The following 3GPP (3rd Generation Partnership Project) documents are incorporated by reference. In particular, they contain details about the terminology used in the present patent application. The documents are publicly available for download from www.3gpp.org.                a) 3GPP Technical Report 25.876 V1.8.0 (2005-10) “Multiple Input Multiple Output (MIMO) antennas in UTRA”, particularly for Double Transmit Antenna Array (D-TxAA).        b) 3GPP Technical Specification 25.212 “Multiplexing and channel coding (FDD)”, particularly for HS-SCCH and DPCCH channel formats.        c) 3GPP Technical Specification 25.214 “Physical Layer Procedures (FDD)”, particularly for Feedback Information (FBI) signalling from UE to BS comprising preferred antenna weights for a BS to use in downlink for closed-loop beamforming. Also for “closed loop mode 1” which is another name for the “TxAA” closed loop beamforming scheme specified in UMTS.        
In 3GPP a proposal called D-TxAA for Double Transmit Antenna Array, is under discussion for UMTS as a way of increasing the peak bit rate. This is derived from an existing closed loop transmit diversity scheme (TxAA mode 1) where the mobile terminal signals to the network indicators of complex weights which should be applied to the signals from each of two transmit antennas. In D-TxAA, two different data streams are transmitted using orthogonal weight vectors, one weight vector being based on those transmitted from the mobile terminal, and the other vector being derived deterministically from the first.
For the operation of D-TxAA, the following may be assumed:                Orthogonal pilot channels are transmitted from each Node B antenna.        No dedicated (i.e. beamformed) pilots are available (assuming that the fractional dedicated physical channel (F-DPCH) is used, which does not carry pilot bits).        Feedback information (FBI) for the first beam is derived by the UE and transmitted to Node B, indicating the desired beamforming vector.        The first beam is transmitted using a restricted code book of weight vectors (for example the codebook currently used for TxAA mode 1).        The identity of the antenna weight vector for the first beam is signalled to the UE on the High-Speed Shared Control Channel (HS-SCCH).        The second beam is transmitted using a deterministic phase vector which is typically orthonormal to the vector for the first beam.        Channel quality information (CQI) is signalled periodically by the UE to the Node B, enabling the Node B to derive a different rate for each of the two beams.        The CQI indicates the rate (or packet size) which can be transmitted successfully (or with a given probability of success) using a reference power level and code resource (the reference values being known by both network and mobile terminal)        The transmissions on the two beams are comprised of separate codewords with potentially different rates.        
In order for the Node B to determine how many codewords can be simultaneously transmitted, it needs information about how many and which beams can support the transmission of a codeword. Typically this is done by CQI reporting, which also includes information about the supportable rate for each codeword. However, frequent CQI reporting results in a high signalling load. A reduced CQI reporting rate may be used, but the Node B will then be slower to react to changes in the rank of the channel, resulting in failed transmissions of codewords on beams, which cannot support transmission, or wasted capacity when beams are not used which could support a transmission.